A known prior art technique for detecting a layer 2 to be detached from a donor substrate 1 and described in U.S. Patent Publication US 2007/0249140 (A1) and shown in FIG. 1, is a method of detaching a layer 2 to be detached from a donor substrate 1, comprising the following steps:                a0) deposition of a metal layer 3 on the donor substrate 1 at a temperature greater than 750° C.,        b0) cooling to room temperature the combination of the donor substrate 1 and the metal layer 3, the cooling causing, by virtue of a difference in the coefficient of thermal expansion, deformation in compression or in tension of the metal layer 3, the deformation of the layer 3 generating a stress in compression or in tension in the donor substrate 1. This stress causes fracture on a fracture plane 4, the fracture plane 4 delimiting the layer 2 to be detached, the stress leading to the detachment of the layer 2 to be detached from the donor substrate 1 on the fracture plane 4.        
After the step a0), a cooling step b0) is applied to the donor substrate 1 covered by the metal layer 3. Cooling leads to the occurrence of a cleaving stress in the donor substrate 1 linked to the difference in the coefficient of thermal expansion between the metal layer 3 and the donor substrate 1.
However, the deposition of a metal layer 3 on the donor substrate 1 risks contamination of the layer 2 to be detached, which compromises the operation of the device fabricated from this layer.
Moreover, the thickness of the layer 2 to be detached depends on the cleavage stress exerted by the metal layer 3. As a result of this, the range of available thicknesses of the layer 2 to be detached is necessarily limited by the characteristics of the available metals.
Furthermore, a detachment method involving differences in the coefficient of thermal expansion that are too low necessitates process temperatures that are too high.
The disclosure, therefore, proposes a method of detaching a layer 2 to be detached from a donor substrate 1 with no risk of contamination of the material of the donor substrate 1 so as to make fracture independent of the differences in the coefficient of thermal expansion.